[PATCH AUTOSEL 6.14 553/642] net-sysfs: prevent uncleared queues from being re-added

Sasha Levin
2025-05-05T22:36:35Z

From: Antoine Tenart <atenart@kernel.org>

[ Upstream commit 7e54f85c60828842be27e0149f3533357225090e ]

With the (upcoming) removal of the rtnl_trylock/restart_syscall logic
and because of how Tx/Rx queues are implemented (and their
requirements), it might happen that a queue is re-added before having
the chance to be cleared. In such rare case, do not complete the queue
addition operation.

Signed-off-by: Antoine Tenart <atenart@kernel.org>
Link: https://patch.msgid.link/20250204170314.146022-4-atenart@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/core/net-sysfs.c | 32 ++++++++++++++++++++++++++++++++
1 file changed, 32 insertions(+)

diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 77465dc3cd648..87b2456aef08a 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -1131,6 +1131,22 @@ static int rx_queue_add_kobject(struct net_device *dev, int index)
struct kobject *kobj = &queue->kobj;
int error = 0;

+ /* Rx queues are cleared in rx_queue_release to allow later
+ * re-registration. This is triggered when their kobj refcount is
+ * dropped.
+ *
+ * If a queue is removed while both a read (or write) operation and a
+ * the re-addition of the same queue are pending (waiting on rntl_lock)
+ * it might happen that the re-addition will execute before the read,
+ * making the initial removal to never happen (queue's kobj refcount
+ * won't drop enough because of the pending read). In such rare case,
+ * return to allow the removal operation to complete.
+ */
+ if (unlikely(kobj->state_initialized)) {
+ netdev_warn_once(dev, "Cannot re-add rx queues before their removal completed");
+ return -EAGAIN;
+ }
+
/* Kobject_put later will trigger rx_queue_release call which
* decreases dev refcount: Take that reference here
*/
@@ -1842,6 +1858,22 @@ static int netdev_queue_add_kobject(struct net_device *dev, int index)
struct kobject *kobj = &queue->kobj;
int error = 0;

+ /* Tx queues are cleared in netdev_queue_release to allow later
+ * re-registration. This is triggered when their kobj refcount is
+ * dropped.
+ *
+ * If a queue is removed while both a read (or write) operation and a
+ * the re-addition of the same queue are pending (waiting on rntl_lock)
+ * it might happen that the re-addition will execute before the read,
+ * making the initial removal to never happen (queue's kobj refcount
+ * won't drop enough because of the pending read). In such rare case,
+ * return to allow the removal operation to complete.
+ */
+ if (unlikely(kobj->state_initialized)) {
+ netdev_warn_once(dev, "Cannot re-add tx queues before their removal completed");
+ return -EAGAIN;
+ }
+
/* Kobject_put later will trigger netdev_queue_release call
* which decreases dev refcount: Take that reference here
*/
--
2.39.5